System and method for communicating using a plurality of TDMA mesh networks having efficient bandwidth use

ABSTRACT

In accordance with a non-limiting example of the present invention, a communications system includes a plurality of Time Division Multiple Access (TDMA) mesh networks, each comprising a plurality of wireless nodes, each having a transmitter and receiver that communicate on a primary and at least one secondary frequency, and communicate using a TDMA epoch that is divided into at least a beacon interval using the primary frequency and a digital data interval using both the primary and secondary frequencies. The wireless nodes are operative for allocating a secondary frequency usage of a digital data interval for a TDMA mesh network to fall into an unused portion of the secondary frequency usage of another TDMA mesh network.

FIELD OF THE INVENTION

The present invention relates to the field of communications, and moreparticularly, to communications over mesh networks.

BACKGROUND OF THE INVENTION

Mesh networking routes data, voice and instructions between nodes andallows for continuous connections and reconfiguration around blockedpaths by “hopping” from one node to another node until a successfulconnection is established. Even if a node collapses, or a connection isbad, the mesh network still operates whether the network is wireless,wired and software interacted. This allows an inexpensive peer networknode to supply back haul services to other nodes in the same network andextend the mesh network by sharing access to a higher cost networkinfrastructure.

Wireless mesh networking is implemented over a wireless local areanetwork using wireless nodes. This type of mesh network is decentralizedand often operates in an ad-hoc manner. The wireless nodes operate asrepeaters and transmit data from nearby wireless nodes to other peers,forming a mesh network that spans large distances. In ad-hoc networking,neighbors find another route when a node is dropped. Nodes can be eitherfixed or mobile, with mobile devices forming a mobile ad-hoc network(MANET) known to those skilled in the art.

The mesh networks use dynamic routing capabilities. A routing algorithmensures that data takes an appropriate and typically the fastest routeto a destination. Some mobile mesh networks could include multiple fixedbase stations with “cut through” high bandwidth terrestrial linksoperating as gateways to fixed base stations or other services,including the internet. It is possible to extend the mesh network withonly a minimal base station infrastructure. There are also manydifferent types of protocols that can be used in a mesh network, forexample, an Ad-hoc On-Demand Distance Vector (AODV), Dynamic SourceRouting (DSR), Optimized Link State Routing protocol (OLSR) andTemporally-Ordered Routing Algorithm (TORA), as non-limiting examples.

Many of the mesh networks operate using a Time Division Multiple Access(TDMA) protocol. Depending on the configuration of a TDMA mesh network,a large portion or even a majority of the configured bandwidth can bewasted. Many of the mesh networks use a primary frequency for a beaconinterval operative as a network control interval and a plurality(sometimes four or more) of secondary frequencies for a digital data(DD) interval. Many of the secondary frequencies can be unused, andthus, as noted before, a large portion or even a majority of theconfigured bandwidth can be wasted.

SUMMARY OF THE INVENTION

In accordance with a non-limiting example of the present invention, acommunications system includes a plurality of Time Division MultipleAccess (TDMA) mesh networks, each comprising a plurality of wirelessnodes. The wireless nodes can comprise a transmitter and receiver thatcommunicate on a primary and at least one secondary frequency andcommunicate with each other using a TDMA epoch that is divided into atleast a beacon interval using the primary frequency and a digital datainterval using both the primary and secondary frequencies. The wirelessnodes are operative for allocating a secondary frequency usage of adigital data interval for a TDMA mesh network to fall into an unusedportion of the secondary frequency usage of another TDMA mesh network.

A TDMA epoch for a second mesh network can be offset from the start of aTDMA epoch for a first mesh network such that TDMA secondary frequencyusage of a digital data interval for the second mesh network falls intoan unused portion of the secondary frequency usage in the first meshnetwork. Each wireless node can be formed as a wireless radio. The startof a TDMA epoch can be maintained for at least two TDMA mesh networks inan overlap condition. The wireless nodes within a TDMA mesh network cancreate a phantom wireless node that hears wireless nodes within anotherTDMA mesh network, whose start of a TDMA epoch is at a desired offsetbased upon an inferred start of a TDMA epoch.

In yet another aspect, the phantom wireless node can be synchronizedwith other wireless nodes within the same TDMKA mesh network. This TDMAepoch can be divided into a beacon interval, a digital voice (DV)interval, and a digital data (DD) interval.

A method aspect is also set forth.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent from the detailed description of the invention whichfollows, when considered in light of the accompanying drawings in which:

FIG. 1 is a block diagram of an example of a communications system thatcan be modified for use with the present invention.

FIG. 2 is a graph showing the frequency use for a single TDMA meshnetwork.

FIG. 3 is a graph similar to FIG. 1, but showing the frequency useoverlap as “bandwidth scavenging” for two TDMA mesh networks, listed asNet 1 and Net 2 in accordance with a non-limiting example of the presentinvention.

FIG. 4 is another graph showing the frequency use overlap as “bandwidthscavenging” for three TDMA mesh networks listed as Net 1, Net 2, and Net3, in accordance with a non-limiting example of the present invention.

FIG. 5 is a chart showing non-express, Quality of Service (QOS) TDMAchannel allocation, and showing how a data packet can travel from asource node A to a destination node E when transmitted by nodes andcrossing the TDMA network.

FIG. 6 is a chart showing an express Quality of Service and End-to-EndLatency (ETEL).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Different embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsare shown Many different forms can be set forth and describedembodiments should not be construed as limited to the embodiments setforth herein Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope to those skilled in the art.

In accordance with a non-limiting example of the present invention,channel wastage can be overcome in a TDMA mesh network communicationssystem by recognizing that a second TDMA mesh network in a non-limitingexample can use the unused TDMA secondary frequencies in a first TDMAmesh network for secondary frequency digital data usage. In effect, thesystem and method can “scavenge” a part of the secondary frequencychannels unused by the first TDMA mesh network, thereby reducing channelwastage.

An example of a communications system that can be used and modified foruse with the present invention is now set forth with regard to FIG. 1.

An example of a radio that could be used with such system and method isa Falcon™ III radio manufactured and sold by Harris Corporation ofMelbourne, Fla. It should be understood that different radios can beused, including software defined radios that can be typicallyimplemented with relatively standard processor and hardware components.One particular class of software radio is the Joint Tactical Radio(JTR), which includes relatively standard radio and processing hardwarealong with any appropriate waveform software modules to implement thecommunication waveforms a radio will use. JTR radios also use operatingsystem software that conforms with the software communicationsarchitecture (SCA) specification (see www.jtrs.saalt.mil), which ishereby incorporated by reference in its entirety. The SCA is an openarchitecture framework that specifies how hardware and softwarecomponents are to interoperate so that different manufacturers anddevelopers can readily integrate the respective components into a singledevice.

The Joint Tactical Radio System (JTRS) Software Component Architecture(SCA) defines a set of interfaces and protocols, often based on theCommon Object Request Broker Architecture (CORBA), for implementing aSoftware Defined Radio (SDR). In part, JTRS and its SCA are used with afamily of software re-programmable radios. As such, the SCA is aspecific set of rules, methods, and design criteria for implementingsoftware re-programmable digital radios.

The JTRS SCA specification is published by the JTRS Joint Program Office(JPO). The JTRS SCA has been structured to provide for portability ofapplications software between different JTRS SCA implementations,leverage commercial standards to reduce development cost, reducedevelopment time of new waveforms through the ability to reuse designmodules, and build on evolving commercial frameworks and architectures.

The JTRS SCA is not a system specification, as it is intended to beimplementation independent, but a set of rules that constrain the designof systems to achieve desired JTRS objectives. The software framework ofthe JTRS SCA defines the Operating Environment (OE) and specifies theservices and interfaces that applications use from that environment. TheSCA OE comprises a Core Framework (CF), a CORBA middleware, and anOperating System (OS) based on the Portable Operating System Interface(POSIX) with associated board support packages. The JTRS SCA alsoprovides a building block structure (defined in the API Supplement) fordefining application programming interfaces (APIs) between applicationsoftware components.

The JTRS SCA Core Framework (CF) is an architectural concept definingthe essential, “core” set of open software Interfaces and Profiles thatprovide for the deployment, management, interconnection, andintercommunication of software application components in embedded,distributed-computing communication systems Interfaces may be defined inthe JTRS SCA Specification. However, developers may implement some ofthem, some may be implemented by non-core applications (i.e., waveforms,etc.), and some may be implemented by hardware device providers.

For purposes of description only, a brief description of an example of acommunications system that could incorporate the “bandwidth scavenging,”in accordance with non-limiting examples of the present invention, isdescribed relative to a non-limiting example shown in FIG. 1. Thishigh-level block diagram of a communications system 50 includes a basestation segment 52 and wireless message terminals that could be modifiedfor use with the present invention. The base station segment 52 includesa VHF radio 60 and HF radio 62 that communicate and transmit voice ordata over a wireless link to a VHF net 64 or HF net 66, each whichinclude a number of respective VHF radios 68 and HF radios 70, andpersonal computer workstations 72 connected to the radios 68, 70. Ad-hoccommunication networks 73 are interoperative with the various componentsas illustrated. Thus, it should be understood that the HF or VHFnetworks include HF and VHF net segments that are infrastructure-lessand operative as the ad-hoc communications network. Although UHF radiosand net segments are not illustrated, these could be included.

The HF radio can include a demodulator circuit 62 a and appropriateconvolutional encoder circuit 62 b, block interleaver 62 c, datarandomizer circuit 62 d, data and framing circuit 62 e, modulationcircuit 62 f, matched filter circuit 62 g, block or symbol equalizercircuit 62 h with an appropriate clamping device, deinterleaver anddecoder circuit 62 i modem 62 j, and power adaptation circuit 62 k asnon-limiting examples. A vocoder circuit 62 l can incorporate the decodeand encode functions and a conversion unit which could be a combinationof the various circuits as described or a separate circuit. These andother circuits operate to perform any functions necessary for thepresent invention, as well as other functions suggested by those skilledin the art. Other illustrated radios, including all VHF mobile radiosand transmitting and receiving stations can have similar functionalcircuits.

The base station segment 52 includes a landline connection to a publicswitched telephone network (PSTN) 80, which connects to a PABX 82. Asatellite interface 84, such as a satellite ground station, connects tothe PABX 82, which connects to processors forming wireless gateways 86a, 86 b. These interconnect to the VHF radio 60 or HF radio 62,respectively. The processors are connected through a local area networkto the PABX 82 and e-mail clients 90. The radios include appropriatesignal generators and modulators.

An Ethernet/TCP-IP local area network could operate as a “radio” mailserver. E-mail messages could be sent over radio links and local airnetworks using STANAG-5066 as second-generation protocols/waveforms, thedisclosure which is hereby incorporated by reference in its entiretyand, of course, preferably with the third-generation interoperabilitystandard: STANAG-4538, the disclosure which is hereby incorporated byreference in its entirety. An interoperability standard FED-STD-1052,the disclosure which is hereby incorporated by reference in itsentirety, could be used with legacy wireless devices. Examples ofequipment that can be used in the present invention include differentwireless gateway and radios manufactured by Harris Corporation ofMelbourne, Fla. This equipment could include RF5800, 5022, 7210, 5710,5285 and PRC 117 and 138 series equipment and devices as non-limitingexamples.

These systems can be operable with RF-5710A high-frequency (HF) modemsand with the NATO standard known as STANAG 4539, the disclosure which ishereby incorporated by reference in its entirety, which provides fortransmission of long distance HF radio circuits at rates up to 9,600bps. In addition to modem technology, those systems can use wirelessemail products that use a suite of data-link protocols designed andperfected for stressed tactical channels, such as the STANAG 4538 orSTANAG 5066, the disclosures which are hereby incorporated by referencein their entirety. It is also possible to use a fixed, non-adaptive datarate as high as 19,200 bps with a radio set to ISB mode and an HF modemset to a fixed data rate. It is possible to use code combiningtechniques and ARQ.

There now follows a more detailed description of at least onenon-limiting example of the “bandwidth scavenging” of the presentinvention. It should be understood that many of the mesh networksoperate using a Time Division Multiple Access (TDMKA) protocol.Depending on the configuration of a TDMA mesh network, a large portionor even a majority of configured bandwidth can be wasted. This can betrue even when considering a maximum possible theoretical channelutilization.

TDMA mesh networks typically include a plurality of wireless nodes thatcommunicate with each other using primary and secondary frequencies andusing TDMA epochs that are divided into a beacon interval operative as anetwork control interval, sometimes a digital voice (DV) interval, and adigital data (DD) interval. For purposes of this description, TDMA meshnetworks use a slot of channel time that is allocated prior to a nodeactually transmitting data during the allocated slot. Details of how theTDMA channel allocation mechanism works is not described in detailbecause it is sufficient that some algorithm is used to allocate apotentially recurring slot of channel time in which a particular nodemay transmit the data. TDMA channel time allocation algorithms typicallysegment channel time into blocks. Each block is an epoch. Blocks aresubdivided into slots used by nodes to transmit data. It is assumed thatthe data to be transmitted constitutes an isochronous stream, meaningthat large portions of data are repeatedly generated and presented atthe source node for delivery to the destination node. The data istypically time dependent, and must be delivered within certain timeconstraints. Multiple frequencies can be allocated to a single TDMA meshnetwork using a primary frequency and a plurality of secondaryfrequencies, sometimes up to four secondary frequencies in non-limitingexamples.

As shown in FIG. 2 for a TDMA mesh network, only the digital datainterval actually uses some of the secondary frequencies. All secondaryfrequencies during the beacon and digital voice intervals are unused.These unused portions of allocated frequencies can be referred to aswasted channel time, or more simply as channel wastage. Depending uponthe relative sizes of the beacon, digital voice and digital dataintervals, and how many secondary frequencies are allocated, a majorityof allocated bandwidth can consist of channel wastage.

Of course, it is possible to configure TDMA mesh networks to minimizechannel wastage. For example, a TDMA mesh network could be configuredusing only the primary frequency and no secondary frequencies, resultingin no channel wastage. Whenever any secondary frequencies are allocated,however, channel wastage occurs. Even in this case channel wastage canbe minimized by maximizing the relative size of the digital datainterval at the expense of any beacon and digital voice interval sizes.Unfortunately, there are practical constraints limiting how much channelwastage can be limited.

Beacon interval size is typically dictated by the number of nodes in theTDMA mesh network, for example, typically wireless nodes and oftenmobile or fixed nodes, as in a mobile ad-hoc network (MANET). More nodesmean a larger beacon interval. Digital voice or video interval size isdictated by the expected peak requirement for simultaneous digital voiceand video services. These digital voice and video intervals can usuallybe reduced below an expected peak need at the cost of failing toprovision the peak need at the likely cost of the digital voice or videofailing to work exactly when it is most needed by the user in the field.

The solution to channel wastage is achieved by recognizing that a secondTDMA mesh network, for example, termed “Net 2” in FIG. 3, can use theunused TDMA portions of the first (“Net 1”) TDMA mesh network'ssecondary frequencies, for its secondary frequency digital data usage.In effect, the system can scavenge a part of the secondary frequencychannels unused by the first TDMA mesh network, thereby reducing channelwastage.

An example of the “bandwidth scavenging” as described is shown in FIG.3. For example, a sixth frequency, f6, is allocated and used as theprimary frequency for the second TDMA mesh network. Its start of epochis offset from the start of epoch for the first TDMA mesh network, suchthat the digital data secondary frequency TDMA usage for the second TDMAmesh network falls in the unused parts of the secondary frequency usagemap of the first TDMA mesh network. In this non-limiting example,channel wastage has been reduced by about 50%.

In accordance with non-limiting examples of the present invention,“bandwidth scavenging” as described requires several functions asfollows:

1. Allocate a new, currently unused frequency for the second TDMA meshnetwork primary frequency;

2. Offset the start of epoch for the second TDMA mesh network from thestart of epoch for the first TDMA mesh network so that the secondaryfrequency usage of the second TDMA mesh network falls in the unusedportion of the secondary frequency usage map of the first TDMA meshnetwork; and

3. Maintain the start of epoch offsets during overlapping operation.

Allocating a new, currently unused frequency such as the primaryfrequency (number 1 above) can be done during the TDMA mesh network'sinitial configuration, or can be accomplished automatically via aconfiguration allowing automatic “bandwidth scavenging” in accordancewith non-limiting examples of the present invention.

Establishing the initial start of epoch offset (number 2 above) can beaccomplished with minimal steps. When a TDMA mesh network, e.g., thesecond TDMA mesh network, hears another mesh network, e.g., the firstTDMA mesh network, with which it wishes to perform bandwidth scavenging,those radios or wireless nodes for the second TDMA mesh network thathear the radios or wireless nodes in the first TDMA mesh network createan artificial, or “phantom” radio or node, whose start of epoch is atthe desired offset based upon the inferred start of epoch for the firstTDMA mesh network. This “phantom” node is included in the second TDMAmesh network node's network synchronization algorithm, i.e., epochsynchronization, beacon synchronization or smoothing algorithm. Theeffect of including this “phantom” node is to gradually andsystematically move the second TDMA mesh network's start of epoch to thedesired offset. Other algorithms to establish the initial start of epochoffset are also possible.

Maintaining a start of epoch offset after the offset was firstaccomplished (number 2 listed above) also takes minimal steps. The“phantom” nodes in the network synchronization algorithm can becontinued.

The “bandwidth scavenging” algorithm as described is flexible regardlessof the configuration of the overlapping TDMA mesh network. This isbecause during the beacon interval only the primary frequency can beused by a TDMA mesh network. Thus, the beacon interval portion of theTDMA mesh network's secondary frequency map is usually available for useby other TDMA mesh networks. As a result, the “bandwidth scavenging” asdescribed can be used, even when the overlapping TDMA mesh network'sdigital voice interval has been eliminated.

Extensions of this type of system are also possible. As part of itscoexistence configuration, a TDMA mesh network can be configured toshift automatically to “bandwidth scavenging” as described whenencountering another TDMA mesh network either to expand its effectivebandwidth or to conserve the overall used bandwidth.

Another extension is to use bandwidth scavenging to overlap more thantwo TDMA mesh networks. An example of this for three TDMA mesh networksis shown in FIG. 4, which shows a chart similar to FIG. 3, but nowshowing a third TDMA mesh network, “Net 3,” which is overlapped byallocating its primary frequency, f7, and aligning this third TDMA meshnetwork's start of epoch to allow its digital data secondary frequencyusage to overlap or fall within the unused portions of the first andsecond TDMA mesh network's secondary frequency usage maps.

In some examples, the available unused secondary frequency gaps are toosmall to fit the alternate third TDMA mesh network's digital datainterval. This is not a serious drawback, and possible alternativemechanisms can handle this situation.

“Bandwidth scavenging” as described is relevant to many RFcommunications devices. Multiple secondary frequencies can be used toextend total radio or wireless node bandwidth, and use the secondaryfrequencies during a digital data interval. As a result, thesefrequencies are wasted during digital voice, digital video, and duringbeacon intervals. “Bandwidth scavenging” as described allows any wastedparts of the secondary frequencies to be used when multiple TDMA meshnetworks are present.

In accordance with a non-limiting example of the present invention, aTDMA type scheme is applied in a coarse-grained fashion to a TDMA meshnetwork radio frequency versus time usage characteristics to allow theseTDMA mesh networks to “scavenge” the unused parts of each other'ssecondary frequencies, by offsetting in time each TDMA mesh network'ssecondary frequency usage with respect to the other(s). Bandwidthscavenging in accordance with a non-limiting example of the presentinvention is used in TDMA mesh networks to accomplish reuse of theotherwise wasted parts of wireless nodes or radio's secondaryfrequencies.

It should be understood that a TDMA mesh network architecture can beformed of different types, and a TDMA epoch in a non-limiting example asset forth comprises a network control interval as a beacon interval anddigital data interval. A network control interval as a plurality ofbeacons uses only the primary frequency. The digital data interval usesboth the primary and secondary frequencies via the TDMA channelallocation.

It is possible to reduce the requirements that any secondary frequencyusage interdigitates, i.e., be non-overlapping. It should be understoodthat multiple TDMA mesh networks should be synchronized. Non-overlappingof secondary frequency usage, while desirable and optimal, is notstrictly required. Thus, non-overlapping secondary frequency usage couldbe shown as an example of a more general inter-meshing networksynchronization.

A “phantom node” synchronization algorithm in accordance withnon-limiting examples of the present invention can allow synchronizationbetween and among multiple mobile, ad-hoc, and TDMA mesh networks.Moreover, there are several ways “bandwidth scavenging” could accomplishinter-network synchronization. Phantom node synchronization is just one.

A “phantom node” synchronization algorithm achieves and maintainssynchronization between and among multiple mobile, ad-hoc, mesh networksindependent from “bandwidth scavenging” as described above in accordancewith non-limiting examples of the present invention. As such, this typeof “phantom node” synchronization algorithm can be useful not just for“bandwidth scavenging” inter-meshed TDMA mesh network synchronization,but also useful when multiple mesh networks should be synchronized forother reasons, e.g., to simplify the job of gateway nodes or simplifythe coexistence and interoperability of multiple TDMA mesh networks onthe same frequency in the same place.

One non-limiting example is a gateway between two high performance TDMAmesh networks that typically communicates using a TDMA epoch that has abeacon interval, digital voice interval, and digital data interval. Thegateway node could be a member of both TDMA mesh networks. The gatewaynode should transmit two beacons, one for each of the two TDMA meshnetworks. If the two TDMA mesh networks are not synchronized, however,problems could arise. For example, sometimes the beacon transmit timesfor the two beacon transmissions will overlap. Because it isunattractive cost-wise to include two independent radios in the gatewaynode, typically a wireless node, the gateway node will be able totransmit one of the two beacons. Moreover, even if the gateway did havetwo independent radios in the one node, when both TDMA mesh networks areoperating on the same frequency, only a single beacon would betransmitted at a time. Otherwise, a collision would occur with theresult that no node would correctly receive either beacon. With the twooverlapping TDMA mesh networks having the same epoch duration, or aninteger multiple thereof, it could be synchronized for simplifying thegateway node's operation. This inter-network gateway functionality is anexample of interoperability.

Coexistence is another example when the system might want to synchronizethe operation of multiple TDMA mesh networks. It is desirable for thebeacon interval of each TDMA mesh network to fall within the digitaldata interval, and in some networks, the digital voice and/or digitaldata interval of the co-located TDMA mesh networks, so that each TDMAmesh network's beacon transmissions would not collide with those of theother TDMA mesh networks. A TDMA mesh network could make an artificialreservation during a digital data interval corresponding to the otherTDMA mesh networks beacon interval. As a result, two TDMA mesh networksprevent any of their nodes from making digital data transmissions orbeacon transmissions that would collide with the other TDMA meshnetworks' beacon transmissions. For a TDMA mesh network to continue tofunction reliably and robustly, many of its beacon transmissions must becorrectly received by neighboring nodes in the TDMA mesh network. Inthis case, synchronization is needed such that these “artificial” TDMAchannel reservations are stationary with respect to the other TDMA meshnetworks' beacon intervals.

“Phantom node synchronization” is a simple and robust technique toachieve synchronization and maintain synchronization between potentiallymultiple TDMA mesh networks, completely independent of the reasons whythe synchronization is desired.

A problem of minimizing end-to-end latency is also addressed inaccordance with non-limiting examples. It should be understood that thetime taken by over-the-air (OTA) headers, inter-frame spaces, cyclicredundancy checks (CRC), trailers, stuff bits, and the like aretypically ignored.

Quality of Service (QoS) parameters are optimized when deliveringreal-time data across a data communications network, and typicallyinclude end-to-end latency, jitter, throughput and reliability. Thedescription as follows focuses on end-to-end latency.

End-to-end latency can be defined as the time it takes to deliver a datapacket from a source node to a destination node. End-to-end latency canalso be defined as the time duration from when the data packet ispresented to the data communications layer of the stack at the sourcenode, to when the data packet is passed up from the data communicationlayer of the stack at the destination node. End-to-end jitter can bedefined as the variance of end-to-end latency, typically expressed asthe standard deviation of latency.

In a multi-hop, ad-hoc, wireless data communications network, a packetwill, in general, be transmitted multiple times, i.e., take multiplehops, as it traverses the network from the source node to thedestination node. For purposes of this description, TDMA mesh networksuse a slot of channel time that is allocated prior to a node actuallytransmitting data during the allocated slot. Details of how the TDMAchannel allocation mechanism works are not described in detail becauseit is sufficient that some algorithm is used to allocate a recurringslot of channel time in which a particular node may transmit the dataTDMA channel time allocation algorithms typically segment channel timeinto blocks. Each block is an epoch. Blocks are subdivided into slotsused by nodes to transmit data. It is assumed that the data to betransmitted constitutes an isochronous stream, meaning that largeportions of data are repeatedly generated and presented at the sourcenode for delivery to the destination node. The data is typically timedependent, and must be delivered within certain time constraints. Forexample, when a data packet traverses the TDMA mesh network from asource node to a destination node, it will be transmitted by somesequence of nodes. For example, this sequence consists of nodes A, B, C,and D to destination node E, where node A is the source node. Forexample purposes, the system assumes each transmitted data packet issuccessfully received by each hop's destination node.

FIG. 5 is a chart illustrating how a particular data packet may travelfrom source node A to destination node E when transmitted by each nodecrossing the TDMA mesh network based upon a non-express-QoS (Quality ofService) TDMA channel allocation algorithm. Each node carrying theisochronous data stream across the TDMA mesh network has been granted aslot by the TDMA algorithm that repeats in each TDMA epoch. During TDMAepoch N, source node A transmits the data packet to node B during thefirst TDMA epoch. Next, during TDMA epoch N+1, node B transmits the datapacket to node C, and node C transmits it to node D. Finally, duringTDMA epoch N+2, node D transmits the data packet to node E, the finaldestination. The end-to-end over-the-air (OTA) latency for the datapacket's traversal is just under two TDMA epochs. OTA latency includesneither stack processing time, the time to travel up/down the stackwithin the source and destination nodes, nor the time the data packetwaits in the queue at the source node for arrival of the source node'sallocated transmission time, which is shown as the first ‘A’ channeltime allocation in TDMA epoch N in FIGS. 5 and 6.

The system analyzes hop latencies that fit together along the routetraversed, with the express Quality of Service (QoS) algorithm asdescribed to reduce end-to-end latency. End-to-end OTA route traversallatency can be substantially reduced by modifying the TDMA channel timeallocation algorithm to order the transmission allocation to each nodeparticipating in the data stream's route within each TDMA epoch as shownin FIG. 6.

Minimum end-to-end latency can be achieved when the next-hop's TxOp(transmission opportunity) for the data stream whose latency the systemis trying to minimize occurs as soon as possible after the QoS datapacket to be relayed is received, ideally at the data slot followingreception. When viewed as a sequence of TxOps, the optimal QoS TxOpsequence consists of a series of adjacent time-sequential TxOps in theepoch, from the source node to destination node, one TxOp for each hop.By paying attention to how hop latencies fit together, and thenoptimally ordering the resulting sequence of channel time allocationswithin the epoch, the end-to-end latency shown in FIG. 6 is reduced toless than half an epoch.

To achieve minimal OTA end-to-end latency, the Express QoS allocationalgorithm can order each node's recurring transmission time within theepoch in route-traversal sequence, i.e., sequentially in the epoch datainterval from a source node to a destination node. This provides themajority of end-to-end OTA latency reduction.

In addition, the Express QOS allocation algorithm can place eachallocation in the route sequence as close as possible to its neighboringallocations in the route sequence. Though not as important as theordering of allocated slots, this provides some additional reduction inend-to-end OTA latency and allows longer routes to fit within singleepoch.

For Express QoS to be able to reduce end-to-end latency, sufficientchannel time, i.e., slots, should be available and unallocated such thatExpress QoS has a choice of allocations at multiple nodes along theroute. The more slot choices Express QoS has available, the more it canminimize end-to-end latency.

The Express QoS allocation algorithm can coordinate local node channeltime allocation across the spatial extent of the source-to-destinationtraversal route. This requires some inter-node communication. Typically,communication between adjacent nodes is required and communicationbeyond adjacent neighbors along the route is not required.

It should be understood that full duplex operation in wireless TDMA meshnetworks is typically achieved by creating two data streams, one streamfor each direction of travel. Express QoS as described requires adifferent ordering of channel allocations for each direction, since anoptimal slot allocation sequence in one direction will be a worst-caseallocation for the opposite direction.

Express QoS as described can substantially reduce the latencyexperienced by packets belonging to a QoS data stream flowing across awireless TDMA “multi-hop” mesh network. This improved QoS latency asdescribed is applicable to demanding QoS-sensitive applications, such astwo-way real-time voice.

To quantify and characterize the latency improvement that can beexpected, consider the expected latency of a packet traveling across awireless TDMA mesh network of diameter “D” from one edge of the networkto the opposite edge. In all cases at each hop the placement of thetransmission slot within the TDMA epoch's digital data interval isentirely dependent upon the details of the operation of the TDMA channelallocation algorithm. Many algorithms are possible. Unless the algorithmexplicitly optimizes relative slot positions along the route so as tominimize the latency experienced by packets traversing that route,however, there is no reason to expect the data packets will achieve an“average” per-hop traversal latency of less than the approximate 0.5TDMA epochs expected by random slot placement. Using the Express QOSTDMA channel allocation algorithm as described, however, per-hoptraversal latency as low as the OTA data transmission time can beachieved provided all allocation can be fit within a single epoch. Asshown in FIG. 6, using Express QoS as described, a data packet cantraverse the entire route in less than a single epoch.

Express QoS is an extension of the TDMA channel allocation algorithm tominimize end-to-end latency along a route across a multi-hop TDMA meshnetwork, adding a latency-minimizing extension to the TDMA algorithm.

It is also possible to use an Optimized Link State Routing (OLSR) insimilar over-the-air (OTA) packet data and exchange link-state routingalgorithms. The OLSR can be adapted to handle multiple waveforms havingdifferent radio ranges by running multiple OLRS processes (MOP), aseparate OLSR process in each node for each of the waveforms. Each OLSRprocess can perform its independent set of HELLO and TC messagetransmissions using a different waveform. Each OLSR process can build amodel of network conductivity, based on its waveform's range, in theusual OLSR fashion.

Each OLSR process can construct a routing table for its waveform'sconductivity and a single composite routing table can be build from thecollection of waveform routing tables Composite routing tables can beconstructed depending upon what routing criteria or combination ofcriteria are optimized. The possible routing criteria can be optimized,including combinations of a minimum number of hops; a minimum end-to-endlatency; a maximum data throughput; congestion avoidance; minimum powerconsumption; a higher reliability such as the fewest dropped packets;and a minimum bandwidth used.

It is also possible to reduce the bandwidth and computational expense.Instead of running a parallel OLSR process in each node for eachwaveform, only a single OLSR process is run in each node. This singleOLSR process can be modified to exchange a separate and independent setof one-hop-neighbor HELLO messages for each waveform. The HELLO messagecould contain only one-hop neighborhood information for that waveform.Each node can build a two-hop neighborhood for each waveform.

The OLSR state table can be extended to segregate link state informationfor each one-hop neighbor by a waveforms. Each node's one-hopneighborhood for each waveform can be distributed in a single TCmessage. This provides each node the information it requires to buildits network topology model of connectivity for each waveform. Thismulti-waveform network topology builds its own composite route table.The improvement merges the multiple OLSR processes of MOP into a singleOLSR process while keeping independent HELLO messaging for eachwaveform. Instead of transmitting separate TC messages for eachwaveform, every waveform's one-hop neighborhood is included in a singleTC message. The bandwidth consumed is significantly reduced, along withthe computational and memory burdens of a separate OLSR process perwaveform and processing of separate TC message data streams for eachwaveform.

Also, OLSR messages can be transmitted using only a “base” waveform thatmay or may not be the longest range waveform. Reception characteristicsof each received OLSR packet on the base waveform are recorded. Aheuristic based upon observed OLSR packet reception characteristics andpreviously characterized relative performance of the different waveformsis used to predict each node's one-hop neighborhood conductivity foreach non-base waveform. It is also possible to performreception-characteristics-to-one-hop-neighborhood inference afterreceiving each node's TC message instead of before generating eachnode's TC message.

This application is related to copending patent applications entitled,“SYSTEM AND METHOD FOR SYNCHRONIZING TDMA MESH NETWORKS,” which is filedon the same date and by the same assignee and inventors, the disclosurewhich is hereby incorporated by reference.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

1. A communications system, comprising: first and second Time Division Multiple Access (TDMA) mesh networks, each comprising a plurality of wireless nodes; each node of the plurality of wireless nodes within respective first and second TDMA mesh networks comprising a transmitter and receiver that communicate on a primary and at least one secondary frequency and using a TDMA epoch that is divided into at least a beacon interval using the primary frequency and a digital data interval using both the primary and secondary frequencies, wherein said wireless nodes allocate an unused secondary frequency such that a digital data secondary frequency TDMA usage for the second TDMA mesh network falls into an unused portion of the secondary frequency usage map of the first TDMA mesh network, wherein a TDMA epoch for the second TDMA mesh network is offset from the start of a TDMA epoch for the first TDMA mesh network such that TDMA secondary frequency usage of the digital data interval for the second TDMA mesh network falls into an unused portion of the secondary frequency usage in the first TDMA mesh network.
 2. The communications system according to claim 1, wherein the start of a TDMA epoch is maintained for at least first and second TDMA mesh networks in an overlapped condition.
 3. The communications system according to claim 1, wherein said wireless nodes within the second TDMA mesh network create a phantom wireless node that hears wireless nodes within the first TDMA mesh network, whose start of a TDMA epoch is at a desired offset based upon an inferred start of a TDMA epoch.
 4. The communications system according to claim 3, wherein said phantom wireless node is synchronized with other wireless nodes within the second TDMA mesh network.
 5. The communications system according to claim 1, wherein said TDMA epoch is divided into a beacon interval, a digital voice interval and a digital data interval.
 6. A method of communicating in a wireless mesh network, which comprises: allocating a primary frequency and at least one secondary frequency within a first TDMA mesh network having a plurality of wireless nodes and communicating with each other using a TDMA epoch that is divided into at least a beacon interval using the primary frequency and digital data interval using both the primary and secondary frequencies; allocating a primary frequency and at least one secondary frequency within a second TDMA mesh network and communicating with each other using a TDMA epoch that is divided into at least a beacon interval using the primary frequency and digital data interval using both primary and secondary frequencies; and allocating an unused secondary frequency in the first TDMA mesh network such that a digital data secondary frequency TDMA usage for the second TDMA mesh network falls into an unused portion of the secondary frequency usage map of the first TDMA mesh network, and further comprising starting a TDMA epoch for the second TDMA mesh network offset from the start of the TDMA epoch for the first TDMA mesh network, wherein the secondary frequency usage of the digital data interval for the second TDMA mesh network falls in an unused portion of secondary frequency usage in the first TDMA mesh network.
 7. The method according to claim 6, which further comprises allocating a new, unused frequency for the primary frequency of the second TDMA mesh network.
 8. The method according to claim 6, which further comprises maintaining the start of TDMA epochs for the first and second TDMA mesh networks in an overlapped condition.
 9. The method according to claim 6, which further comprises allocating a primary frequency and at least one secondary frequency within a third TDMA mesh network having a digital data interval on at least one secondary frequency, wherein the TDMA secondary frequency usage of the digital data interval falls in an unused portion of the secondary frequency usage of first and second TDMA mesh networks.
 10. The method according to claim 6, which further comprises creating a phantom wireless node from wireless nodes within the second mesh network that hear wireless nodes within the first TDMA mesh network, whose start of a TDMA epoch is at a desired offset based upon an inferred TDMA mesh network start of a TDMA epoch.
 11. The method according to claim 10, which further comprises creating the phantom wireless node when synchronizing the second TDMA mesh network.
 12. The method according to claim 11, which further comprises establishing a plurality of phantom wireless nodes when synchronizing the second TDMA mesh network.
 13. The method according to claim 6, which further comprises encountering a third TDMA mesh network such that TDMA secondary frequency usage for the third TDMA mesh networks falls in an unused portion of the first and second TDMA mesh networks that have been encountered.
 14. The method according to claim 6, which further comprises dividing the TDMA epoch into a beacon interval, and optional digital voice interval and a digital data interval.
 15. A method of communicating in a Time Division Multiple Access (TDMA) wireless mesh network, which comprises: allocating a primary frequency and at least one secondary frequency within first and second TDMA mesh networks, each having a plurality of wireless nodes and communicating with each other using a TDMA epoch that is divided into at least a beacon interval using the primary frequency and a digital data interval using both the primary and secondary frequencies; and allocating by the first TDMA network an unused secondary frequency such that a digital data secondary frequency TDMA usage for the second TDMA mesh network falls in an unused portion of the secondary frequency usage of the first TDMA mesh network, and further comprising starting a TDMA epoch for the second TDMA mesh network offset from the start of the TDMA epoch for the first TDMA mesh network, wherein the secondary frequency usage of the digital data interval falls in an unused portion of secondary frequency usage in the first TDMA mesh network.
 16. The method according to claim 15, which further comprises allocating a new, unused frequency for the primary frequency of the second TDMA mesh network.
 17. The method according to claim 15, which further comprises maintaining the start of TDMA epochs for first and second TDMA mesh networks in an overlapped condition.
 18. The method according to claim 15, which further comprises creating a phantom wireless node from wireless nodes within the second TDMA mesh network that hears wireless nodes within the first TDMA mesh network, whose start of a TDMA epoch is at a desired offset based upon an inferred TDMA start of a TDMA epoch of the first TDMA mesh network.
 19. The method according to claim 15, which further comprises creating the phantom wireless node when synchronizing the second TDMA mesh network.
 20. The method according to claim 19, which further comprises establishing a plurality of phantom wireless nodes that are created when synchronizing the second TDMA mesh network.
 21. The method according to claim 15, which further comprises dividing the TDMA epoch into a beacon interval, and optional digital voice interval and a digital data interval. 